High-frequency unsteady flow near the tip in a transonic fan rotor with a small clearance

AbstractIn this paper, a double-passage shape correction (DPSC) method is presented for simulation of unsteady flows around vibrating blades and aeroelastic prediction. Based on the idea of phase-lagged boundary conditions, the shape correction method was proposed aimed at efficiently dealing with unsteady flow problems in turbomachinery. However, the original single-passage shape correction (SPSC) may show the disadvantage of slow convergence of unsteady solutions and even produce nonphysical oscillation. The reason is found to be related with the disturbances on the circumferential boundaries that can not be damped by numerical schemes. To overcome these difficulties, the DPSC method is adopted here, in which the Fourier coefficients are computed from flow variables at implicit boundaries instead of circumferential boundaries in the SPSC method. This treatment actually reduces the interaction between the calculation of Fourier coefficients and the update of flow variables. Therefore a faster convergence speed could be achieved and also the solution stability is improved. The present method is developed to be suitable for viscous and turbulent flows. And for real three-dimensional (3D) problems, the rotating effects are also considered. For validation, a 2D oscillating turbine cascade, a 3D oscillating flat plate cascade and a 3D practical transonic fan rotor are investigated. Comparisons with experimental data or other solutions and relevant discussions are presented in detail. Numerical results show that the solution accuracy of DPSC method is favorable and at least comparable to the SPSC method. However, fewer iteration cycles are needed to get a converged and stable unsteady solution, which greatly improves the computational efficiency.

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Steady and Unsteady Flow Field at Pump and Turbine Exits of a Torque Converter

Journal of Fluids Engineering ◽

10.1115/1.2820696 ◽

1998 ◽

Vol 120 (3) ◽

pp. 538-548 ◽

Cited By ~ 16

Author(s):

Y. Dong ◽

B. Lakshminarayana ◽

D. Maddock

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Frequency Response ◽

High Frequency ◽

Free Stream ◽

Torque Converter ◽

Flow Data ◽

High Frequency Response ◽

The Core ◽

Measurement Plane

The steady and unsteady flow field at the pump and the turbine exit of a 245 mm diameter automotive torque converter was measured by a miniature high-frequency-response five-hole probe and a high-frequency-response total pressure Pitot probe in the stationary reference frame. The data were decomposed into blade periodic, blade aperiodic, and unresolved unsteady components. The periodic flow data shows that the pump exit flow has four major zones; the free-stream flow, the blade wake flow, the core-suction corner separation flow, and the mixing zone. The unsteady flow data shows that the unsteadiness in the free-stream is uniform, and the unsteadiness in the wake mixing flow zone is very high. The turbine exit flow is almost fully developed at the measurement plane, the flow field is uniform in the tangential direction, and only radial gradients in flow properties exist. A region of separated flow with high unsteadiness and high axial component of vorticity was observed at the measurement plane near the core.

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Drag force acting on a neuromast in the fish lateral line trunk canal. I. Numerical modelling of external–internal flow coupling

Journal of The Royal Society Interface ◽

10.1098/rsif.2008.0291 ◽

2008 ◽

Vol 6 (36) ◽

pp. 627-640 ◽

Cited By ~ 14

Author(s):

Charlotte Barbier ◽

Joseph A.C. Humphrey

Keyword(s):

Unsteady Flow ◽

Lateral Line ◽

High Frequency ◽

External Flow ◽

Vortical Flow ◽

Navier Stokes ◽

Coupled Flow ◽

Pass Filter ◽

Low Pass Filter ◽

Drag Forces

Fishes use a complex, multi-branched, mechanoreceptive organ called the lateral line to detect the motion of water in their immediate surroundings. This study is concerned with a subset of that organ referred to as the lateral line trunk canal (LLTC). The LLTC consists of a long tube no more than a few millimetres in diameter embedded immediately under the skin of the fish on each side of its body. In most fishes, pore-like openings are regularly distributed along the LLTC, and a minute sensor enveloped in a gelatinous cupula, referred to as a neuromast, is located between each pair of pores. Drag forces resulting from fluid motions induced inside the LLTC by pressure fluctuations in the external flow stimulate the neuromasts. This study, Part I of a two-part sequence, investigates the motion-sensing characteristics of the LLTC and how it may be used by fishes to detect wakes. To this end, an idealized geometrical/dynamical situation is examined that retains the essential problem physics. A two-level numerical model is developed that couples the vortical flow outside the LLTC to the flow stimulating the neuromasts within it. First, using a Navier–Stokes solver, we calculate the unsteady flow past an elongated rectangular prism and a fish downstream of it, with both objects moving at the same speed. By construction, the prism generates a clean, periodic vortex street in its wake. Then, also using the Navier–Stokes solver, the pressure field associated with this external flow is used to calculate the unsteady flow inside the LLTC of the fish, which creates the drag forces acting on the neuromast cupula. Although idealized, this external–internal coupled flow model allows an investigation of the filtering properties and performance characteristics of the LLTC for a range of frequencies of biological interest. The results obtained here and in Part II show that the LLTC acts as a low-pass filter, preferentially damping high-frequency pressure gradient oscillations, and hence high-frequency accelerations, associated with the external flow.

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Unsteady flow of a viscous gas between two solid walls, one of which is free and vibrating at high frequency

Fluid Dynamics ◽

10.1007/bf01015065 ◽

1973 ◽

Vol 6 (2) ◽

pp. 275-280

Author(s):

V. A. Biushkin ◽

S. G. Dadaev ◽

G. A. Zav'yalov

Keyword(s):

Unsteady Flow ◽

High Frequency ◽

Viscous Gas ◽

Solid Walls

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Transonic Fan Tip-Flow Features Revealed by High Frequency Response Over-Tip Pressure Measurements

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50279 ◽

2008 ◽

Cited By ~ 2

Author(s):

Hyoun-Woo Shin ◽

William Solomon ◽

Aspi Wadia

Keyword(s):

Frequency Response ◽

High Frequency ◽

Pressure Rise ◽

Tip Leakage Flow ◽

Complex Flow ◽

Phase Lock ◽

Pressure Transducers ◽

High Frequency Response ◽

Wall Boundary Layer ◽

Transonic Fan

Data from an array of high frequency response pressure transducers embedded in the casing wall over the tip of a transonic fan are reported. Phase-lock averaging of data from this array was successful in resolving an axial-tangential map of the static pressure rise in the rotor tip, as has been reported by other workers. Phase-lock ensemble RMS processing of the data is shown to be a useful technique that provides insight into the flow physics around the blade tip. Comparison with CFD results allows for more definite identification of features observed in the data. A complex flow field involving the casing wall boundary layer, the blade shock system and the over-tip leakage flow is observed. Differences between CFD data and measurements are explored by way of computational sensitivity studies. Results are reported for a range of throttle settings and speeds.

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Investigation of Unsteady Flow in a Submersible Tubular Pumping System

Volume 3: Fluid Machinery; Erosion, Slurry, Sedimentation; Experimental, Multiscale, and Numerical Methods for Multiphase Flows; Gas-Liquid, Gas-Solid, and Liquid-Solid Flows; Performance of Multiphase Flow Systems; Micro/Nano-Fluidics ◽

10.1115/fedsm2018-83062 ◽

2018 ◽

Author(s):

Yan Jin ◽

Hongcheng Chen ◽

David S.-K. Ting ◽

Jacqueline Stagner ◽

Junxin Wu ◽

...

Keyword(s):

Unsteady Flow ◽

Cross Sections ◽

High Frequency ◽

Pressure Pulsation ◽

Guide Vane ◽

Flow Characteristics ◽

Pulsation Frequency ◽

Cfd Simulations ◽

Pumping System ◽

Unsteady Interaction

To better understand the workings of submersible tubular pumping system and to enable future improvements, the pressure fluctuation and unsteady flow characteristics due to the complex rotor-stator interactions need to be properly delineated. High-frequency pressure measurements coupled with CFD simulations have been invoked in this study to elucidate the unsteady flow in different components of a submersible tubular pumping system at different discharges. The focus is on the impeller and guide vane, where the unsteady interaction is the strongest. The pressure pulsation distributions of different characteristic cross sections such as impeller exit, middle of guide vane, and exit of guide vane were quantified. In addition, the flow characteristics and the turbulent kinetic energy inside the impeller, guide vane, and bulb unit were obtained at the different time steps. The results show that the pressure pulsation frequency obtained by simulation was in agreement with the experimental results, including the critical points around the impeller and the guide vanes. The complementary two-prong approach is thus proven to be a powerful duo in researching and advancing a convoluted pumping system.

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A High-Frequency-Response Pressure Probe for the Measurement of Unsteady Flow Between Two Rotors in a Hydrodynamic Turbomachine

Volume 1: Turbomachinery ◽

10.1115/96-gt-412 ◽

1996 ◽

Author(s):

C. Achtelik ◽

J. Eikelmann

Keyword(s):

Unsteady Flow ◽

Frequency Response ◽

High Frequency ◽

Torque Converter ◽

Pressure Probe ◽

Ensemble Averaging ◽

Probe Diameter ◽

High Frequency Response ◽

Single Sensor ◽

Response Pressure

A new, specially-developed high-frequency-response pressure probe was used to measure the unsteady flow in the interaction region between the pump and the turbine in a hydrodynamic torque converter. In order to reduce the probe diameter, a single-hole, single-sensor cylindrical probe (⌀=1.33mm) was developed, to replace the standard multi-hole probe. The smaller the probe the higher the accuracy in unsteady flow. Therefore this is an improvement over three-hole probe. Three-hole probe measurements were simulated by recording data in three different angular positions. The time variable velocity vectors were determined using the probe’s calibration coefficients and the knowledge of the rotor positions (measured by angle-encoders) for every measurement value. During the data processing, a double ensemble averaging was carried out, taking into account the positions of the pump and the turbine.

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Study of Near-Stall Flow Behavior in a Modern Transonic Fan With Compound Sweep

Journal of Fluids Engineering ◽

10.1115/1.4006878 ◽

2012 ◽

Vol 134 (7) ◽

Cited By ~ 16

Author(s):

Chunill Hah ◽

Hyoun-Woo Shin

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Flow Structure ◽

Flow Behavior ◽

Pressure Rise ◽

Tip Clearance ◽

The Other ◽

Other Hand ◽

Transonic Fan ◽

Tip Clearance Vortex

Detailed flow behavior in a modern transonic fan with a compound sweep is investigated in this paper. Both unsteady Reynolds-averaged Navier-Stokes (URANS) and large eddy simulation (LES) methods are applied to investigate the flow field over a wide operating range. The calculated flow fields are compared with the data from an array of high-frequency response pressure transducers embedded in the fan casing. The current study shows that a relatively fine computational grid is required to resolve the flow field adequately and to calculate the pressure rise across the fan correctly. The calculated flow field shows detailed flow structure near the fan rotor tip region. Due to the introduction of compound sweep toward the rotor tip, the flow structure at the rotor tip is much more stable compared to that of the conventional blade design. The passage shock stays very close to the leading edge at the rotor tip even at the throttle limit. On the other hand, the passage shock becomes stronger and detaches earlier from the blade passage at the radius where the blade sweep is in the opposite direction. The interaction between the tip clearance vortex and the passage shock becomes intense as the fan operates toward the stall limit, and tip clearance vortex breakdown occurs at near-stall operation. URANS calculates the time-averaged flow field fairly well. Details of measured rms static pressure are not calculated with sufficient accuracy with URANS. On the other hand, LES calculates details of the measured unsteady flow features in the current transonic fan with compound sweep fairly well and reveals the flow mechanism behind the measured unsteady flow field.

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The Microstructure of Steatite (Protoenstatite)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118102 ◽

1985 ◽

Vol 43 ◽

pp. 236-237

Author(s):

W. E. Lee ◽

A. H. Heuer

Keyword(s):

High Frequency ◽

Glass Ceramics ◽

Magnesium Silicate ◽

Beam Current ◽

Glassy Matrix ◽

Angle Of Incidence ◽

X Ray ◽

Mechanical And Electrical Properties ◽

Argon Ions ◽

High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

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